1. Field of the Invention
The present invention relates to a circuit film and a display device including the same, for example, a liquid crystal display device.
2. Description of the Background Art
To drive a liquid crystal display device, a driver IC (integrated circuit) is mounted so as to be connected to lines on a liquid crystal panel. Examples of a method for mounting a driver IC include COG (Chip On Glass) technology wherein a driver IC is directly mounted on a glass substrate such that an electrode of the driver IC is connected to a wire on the glass substrate and SOF (System On Film) technology wherein a driver IC is mounted on a flexible printed circuit (FPC) and connected to a liquid crystal panel (see Japanese Patent No. 3154810). Further, a peripheral circuit mounting process is performed wherein a liquid crystal panel having a driver IC mounted thereon is connected to a control board having other circuits mounted thereon, e.g., a driver IC controller, a power supply circuit, etc.
FIG. 9 is a perspective view schematically showing a conventional FPD (flat panel display). In the FPD shown in FIG. 9, a control board 210 is placed on a back surface of a backlight unit 200, and a SOF (System On Film) 220 connected to the control board 210 is connected to a panel. However, as the thickness of a panel guide or the backlight unit 200 increases along with the increase in size of the FPD, it is necessary to elongate the SOF 220 in order to place the control board 210 on the back surface. Accordingly, the area of a film substrate of the SOF 220 increases, and the cost is inevitably increased. Further, since the exterior size of the control board 210 increases, the number of boards which can be cut out from a mother board is decreased, and as a result, the cost is increased.
In view of such, a recently-employed method is such that a portion of a board to which a SOF is connected is separated from a control board, and the separated portion of the board is placed at a side of a backlight unit. With this method, even if the thickness of the backlight unit is increased, elongation of the SOF can be avoided.
FIG. 10 is a plan view schematically showing a board-separated FPD. FIG. 11 is a perspective view of the board-separated FPD. It should be noted that a source SOF 120 and an input FPC 160 are omitted from FIG. 11.
At the periphery of a liquid crystal display panel, the source SOF 120 including a source driver IC 121 mounted thereon and a gate SOF 130 including a gate driver IC 131 mounted thereon are connected. The source SOF 120 and the gate SOF 130 are connected to a source board 140 and a gate board 150, respectively. The source board 140 and the gate board 150 are connected to a control board 180 through the input FPCs 160 and 170, respectively. The input FPCs 160 and 170 are connected to the boards 140, 150 and 180 by connectors 141, 151, 181 and 182 formed thereon. The control board 180 is placed on a back surface of a backlight unit 110. The boards 140 and 150, which are separated from the control board 180, are placed in a dead space at a side of the backlight unit 110. As a result, the exterior of the control board 180 is optimized, and the board area is reduced. Accordingly, the increase in cost is suppressed. Further, elongation of the SOFs 120 and 130 is avoided, and the cost is decreased.
However, since the control board 180 is separated from the boards 140 and 150, it is necessary to additionally provide an exclusive interface for connecting these separated elements (for example, a FPC, a flexible flat cable, etc.). Adding this interface causes another problem, i.e., an increase in cost. Specifically, the input FPCs 160 and 170 are necessary, and accordingly, the connectors 141, 151, 181 and 182 for connecting the input FPCs 160 and 170 to the boards 140, 150 and 180 are also necessary.